1. Field of the Invention
The present invention relates to a method and apparatus for plasma processing a substrate, and more particularly to an in-situ method and apparatus for determining an etch property of a layer on a substrate during a plasma etch process.
2. Discussion of the Background
The fabrication of integrated circuits (IC) in the semiconductor device manufacturing industry typically employs plasma to create and assist surface chemistry necessary to remove material from and to deposit material to a substrate. In general, plasma is formed within a plasma processing system under vacuum conditions by heating electrons to energies sufficient to sustain ionizing collisions with a supplied process gas. Moreover, the heated electrons can have energy sufficient to sustain dissociative collisions and, therefore, a specific set of gases under predetermined conditions (e.g., chamber pressure, gas flow rate, etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the processing system (e.g., etching processes during which materials are removed from the substrate or deposition processes during which materials are added to the substrate). During, for example, an etch process, monitoring the etch rate and the spatial uniformity of the etch rate can be very important when determining the state of a plasma processing system and for qualifying such a system following a maintenance interval. In current manufacturing practice, system qualification is usually performed by executing a series of qualification substrates and measuring the resultant etch rate and etch rate uniformity to determine whether to continue production or to perform system maintenance such as a wet clean of the process chamber. Furthermore, the method of determining the etch rate and the uniformity of the etch rate involves substrate cleaving (i.e. sacrifice of the substrate), and SEM (scanning electron microscope) analysis. Using SEM micrographs, feature etch depths can be measured at different locations on the qualification substrates and, when combined with the etch time, information for etch rate and etch rate uniformity can be acquired.
Consequently, significant system production time is expended and qualification substrates are consumed, hence, leading to greater production costs during the tedious qualification process. Moreover, production substrates and qualification substrates can differ substantially and, therefore, lead to erroneous conclusions regarding system qualification. For example, the measured etch rate on qualification substrates does not necessarily reflect the real etch rate on the production wafer.